Thermostatic element



Sept. 24, 1929. w, M, CHACE Y 'i 1,729,245

THEnMosTATIc; ELEMENT Filed Dec. 19, 1927 I man Jaa A TTORNE Y.

Patented Sept`. 24, 1929 UNITED STATES r v1,729,245v

APATaN'r oFF'lcEQ,

WILLIAM M. CHACE, OF DETROIT, MICHIGAN; ADELBERT E. LINDLEY, ABTUECOOPER, AND HILMA B. CHACE, EXECUTORS OF SAID WILLIAM IL OHACE, DE-CEASED, ASSIGNORS T W. M. OHACE VALVE COMPANY, OF DETROIT, MICHIGAN,

A CORPORATION OF MICHIGAN THERMOSTATIC ELEMENT Application illedDecember 19, 1927. Serial No. 241,275.

This invention relates to bimetallic elements such as are ordinarilyused in various positions where it is subjected to variation 1ntemperature and to perform work by 1ts 5 consequent transientdeformation as 1n the making and breaking of the electric circuit l orVcontrol of various devices, and the purpose of the invention is tosecure abimetallic element in which the greatest movement is within atemperature range of from about 400 to 700 degrees F., and that is lessresponsive to temperature change below or above such temperature rangeand further one that may be subjected to high temperature withoutpermanent deformation.

The accompanying drawing is a diagram illustrating the expansion curveof my improved thermostatic couple.

Various efforts have been made in the past to secure a bimetallicelement having such characteristics the purpose being to secure'a devicethat is very rapid in movement through the temperature range in whichits movement is to be utilized and has little or no movement attemperatures outside of said range. For instance, in an electric iron, abimetallic disk is used to make and break the circuit but if the disk ismade of two elements liable to permanent deformation at temperatures inthe neighborhood of 500 degrees F., the device is of short-life andtherefore not practical to use at such temperatures, and again forinstance in a thermostatio spark plug, one of the electrodes being madeof a bimetallic element which is subject to the heat developed in thecylinder of an internal combustion engine, it is not desirable for thethermostatic electrode to materially move from close association withthe other fixed electrode until it has attained a temperature above 400degrees F., and must not be subject to permanent deformation attemperatures around 2000 degrees F., in continued operation of theengine.

The commonly known invar and brass bimetallic element is not eliicientfor this purpose although sensitive at temperatures below 500 degreesF., and it is also known that certain nickel steels having a greaterdifference of expansion than the invar-brass combination butthe knowncomposition of nickel steels such for instance as described in the U. S.atent to Miller, No. 1,604,064 o r my own atent No. 1,642,485 are suli-vciently rapid in movement at tem eratures above 500 degrees F. Whilesuch b ades are effective for some purposes they are uneffective wherethe movement is desired to be" as constant er degree of temperaturechange 500 to 700 egrees F., as they are from 400 60 to 500 degrees F. i

In the research and experimental vwork to find a composition of elementsfor the eX- pansion side of a bimetallc b1ade-or plate, I havediscovered that the nickel content may lbe reduced below that disclosedin either of the U. S. patents above mentioned and the chromium andcopper increasedfrelative to the percentage thereof disclosed in my saidformer patent and still secure a composition of practically the samecoefficient of expansion and secure movement through a higher range oftemperature than has here-` tofore been attained. This composition iswelded to an element containing approximately forty per cent of nickeland being more sensitive to `temperature change than invar, counteractsthe tendency of the expansion element to cause movement or restrictingsuch movement until the desired 80 temperature is attained whereupon themovement is rapid through the described temperature range. A bimetallicelement having the' described characteristics may be formed of twoplates, blades,'or sheets of metal of the 85 following respectivecompositions welded together. The neutral side preferably consists of-Carbon-; s 35 Silicon 2.00 Nickel 40. 00 Iron 57. 65 and the expansionside consists of- Carbon .25 tol .35 Silicon 1.75 to 2. 00 Chromium 13.25 to 14. 00 Nickel 2. 50 to 3. 50 Copper 5. 00 to 7. 00

Wrought iron l 77.25 to 73.15

The elements above enumerated are the usual named elements of commerceand the iron utilized (particularly in the expansion element) ispreferably what is known to the trade as Swedish iron'because of ltspurity and containing a trace of copper.

The elements comprising the expansion side are given to indicat thepresent known ermissible variation in q antity of each.

This bimetallic element has the characteristics as is shown in theaccompanyine ldiagram by the heavy line. The horizonta lines of thediagram represent inches of movement while the vvertical lines are thetemperature lines under which the movement takes place,

of bimetallic strips of a size .048 inches thick;

by 1/2 inch wide by 5 1/8 inches long. It will be apparent from thediagram that, with such a strip held stationary at one end, the movementat the opposite or free end through temperature of 350 degrees F., isapproximately 4/10 of an inch and for each l100 degrees o change intemperature from 350 to 70 0 degrees F., and that the movement ispractically 4/10 of an inch and therefore is practically constant foreach 100 degrees change up to 700 degrees, and that from 700 to 800degrees the movement is only about 1/10 of an inch. Thus, by use of mynew composition for the expansion side in conjunction with an elementcontaining approximately 40 per cent of nickel I obtain a bimetallicelement that has very little movement below 300 degrees F., or above 700degrees F., and that the movement is very rapid and practically constantfor each de ree of change in a temperature range of rom about 350 yto700 degrees F.

Due to the fact that movement in the bimetallic strip or plate is causedby reason of the difference in coelcient of expansion of the twoelements forming the same, I believe the peculiar movement curve of mynew element is secured by reason of the fact that what I have termed theneutral side does not have a xed coefficient of expansion throughout thetemperature range described but on the contrary, expands to a degreeapproximating that of the expansion side up to 350degrees F., and from350 to about 700 degrees has very little or no expansion and above thesaid temperature expands on to a degree more' closely approximating thatof the expansion side. That this is strictly the fact, however, I amunable to determine inasmuch as the expansionside of the element alsomay have a coeilicient o expansion varying under the different degreesof heat to which it is subjected.

A bimetallic element of two plates or blades of the respectivecompositions mentioned iscapable of withstanding temperatures as high as2000 degrees F., without permanent deformation or loss of elasticity,and the preferable method of securing the two parts together is by lirstwelding with a flux between the plates and then rolling the same whilehot. Subsequent to the rolling operation, the bimetallic sheet may becut into blades, strips or plates or" other forms depending upon thepurpose for or the device with which the element is to be utilized.

Havin thus full described my invention, what I c aim and esire to secureby Letters Patent of the United States is- 1. A bimetallic thermometerconsisting of two metal parts welded together, one of said partsconsistin of the following elements vapproximately o the statedpercentage-viz,

. 35 VSilicon 2. 00 Nickel 40. 00 Iron 57.

and the other part consisting of the following elements approximately ofthe percentage 2. A bimetallic thermometer capable of being subjected totemperatures as high as 2000 degrees F., without permanent deformationconsisting of two metal parts welded together in a unitary structure andcharacterized by having pronounced dissimilar thermal characteristicswithin a specic ytemperature range, one of the parts consisting of thefollowing ingredients substantially in the percentage stated- Carbon 35Silicon 2. 00 Nickel 40 0() Iron 57. 65

and the other consisting of theffollowing ingredients within thespecified percentage range-namely,

Carbon .25 to ..35 Silicon 1.75 to 2.00 Chromium 13. 5 to 14.00 Nickel2. 50 t0 3. 50 Copper i 5. 00 to 7. 00 Wrought iron 77.25 to 73. 15

ioo

(ill

expansion being formed of the following ingredients.-

Carbon .25 to .35

Silicon 1.75 to 2.00 Chromium 13.25 to 14. 00 Nickel 2. 50 to 3. 50Copper 5. 00 to 7. 00 Wrought iron A.; 77.25 to 73. 15

4. A bimetallic thermometer consisting of two nickel `steel elementssecured together to form a unitary structure, one of the elementscontaining approximately 4 0 per cent of nickel and the other containingapproximately 3 per cent of nickel and approximately 14y per cent ofchromium, the structure being tion.

WILLIAM M. CHACE.

